Buffalo Arms sells or sold .50/70 brass as well as .50 Alaskan brass.
I've made .50/70 brass out of .577 Exp. and .348 cases. I lucked out with my .50/70 barrel being an original 1867 contract lined .54 percussion barrel. This had a 1.9" straight taper chamber, not the normal .50/70's 1 3/4" bl.
My best load (22" carbine bl.) was a 450gr. bullet with 10gr. IMR3031 and 60gr. 2F GOEX. 3" at 100 meters.
The .50 Alaskan has a 2.1" case length. With a paper patched to bore size bullet, the case (Starline) will hold a full 91gr. Swiss 1 1/2 FG. That will get it rockin'. With a 550gr. RCBS bullet, the .50 Alaskan will hold 86gr. 2F GOEX in my .348 cases.
I didn't get around to chronographing my load.